1. Field of the Invention
The present invention relates generally to bar code symbol reading systems and, more specifically, to systems having one or more base stations and one or more hand-held bar code symbol readers equipped to communicate with these base stations.
2. Brief Description of the Prior Art
Bar code symbols have become widely used in many commercial environments including point-of-sale (POS) stations in retail stores and supermarkets, inventory and document tracking, and diverse data control applications. To meet the growing demands of this technological innovation, bar code symbol readers of various types have been developed for scanning and decoding bar code symbol patterns, and for producing symbol character data to be used as input in automated data processing systems.
In general, prior art hand-held bar code symbol readers using laser scanning mechanisms can be classified into two major categories. The first category includes manually-actuated trigger-operated systems having lightweight laser scanners which can be held in a user's hand. The user positions the hand-held laser scanner at a specified distance from an object bearing a bar code symbol. Next, the user manually activates the scanner to initiate reading, and then moves the scanner over other objects bearing bar code symbols to be read. Prior art bar code symbol readers illustrative of this first category are disclosed in U.S. Pat. Nos. 4,387,297 to Swartz; 4,575,625 to Knowles; 4,845,349 to Cherry; 4,825,057 to Swartz, et al.; 4,903,848 to Knowles; 5,107,100 to Shepard, et al.; 5,080,456 to Katz, et al.; and 5,047,617 to Shepard, et al.
The second category of hand-held laser-based bar code symbol readers includes automatically actuated systems having lightweight triggerless hand-held laser scanners which can be supported in the hand of the user. The user positions the hand-held laser scanner at a specified distance from the object bearing the bar code, whereupon the presence of the object is automatically detected. The presence of the bar code symbol on the object is also detected, and thereafter the detected bar code symbol automatically read. Prior art illustrative of this second category of laser-based bar code symbol reading systems are disclosed in U.S. Pat. Nos. 4,639,606 to Boles, et al., and 4,933,538 to Heiman, et al.
Presently, there are basically two methods of interconnecting a hand-held laser-based bar code scanner to a base station which, depending on the particular application, may be either a controller, a keyboard-scanner interface device, or a central or host computer. The first method of interconnection employs physical wiring between each hand-held bar code scanner and an associated base unit. Typically, the physical wiring is realized as flexible cord having a coiled structure to permit elongation as required during bar code symbol reading operations.
A major drawback with bar code symbol reading systems using the physical-wiring method of interconnection is that the movement of the portable hand-held laser scanning device is restricted by the overall (extended) length of the flexible cord. In many applications, such as product inventory, the use of such bar code symbol reading systems is simply unacceptable. The second method of interconnection employs a “wireless” electromagnetic communication link between each hand-held bar code scanner (or reader) and its associated base unit. Typically, the electromagnetic communication link is established by transmitting and receiving electromagnetic signals over the radio-frequency (RF) or infra-red (IR) region of the electromagnetic spectrum. Examples of such systems are disclosed in U.S. Pat. Nos. 4,418,277 to Tremmel, et al. and 5,157,687 to Tymes, and in the U.S. Patents cited therein.
While prior art bar code symbol reading systems employing the wireless method of interconnection offer a marked degree of flexibility over systems utilizing the physical wiring method, such systems nevertheless suffer from a number of shortcomings and drawbacks. In particular, these systems require two-way packet communications which involves the use of complex data communications protocols and a separate transmitter and a receiver (i.e., transceiver) at each hand-held bar code symbol reader and base unit in the system. Typically, these data communications requirements increase the cost of manufacture of such systems, and substantially increase the electrical power consumed by each hand-held bar code symbol reader.
Thus, there is a great need for a bar code symbol reading system and method which overcomes the above-described shortcomings and drawbacks without compromising system performance and versatility.